Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$31.53	5.356%	$33.2187	$33.22	$33.20	$33.20
Purchase #2	$129.83	6.236%	$137.9262	$137.93	$137.95	$137.90
Purchase #3	$56.41	11.596%	$62.9513	$62.95	$62.95	$63.00
Purchase #4	$78.70	13.430%	$89.2694	$89.27	$89.25	$89.30
Purchase #5	$142.87	6.255%	$151.8065	$151.81	$151.80	$151.80
Purchase #6	$12.94	7.790%	$13.948	$13.95	$13.95	$13.90
Purchase #7	$89.99	4.589%	$94.1196	$94.12	$94.10	$94.10
7 purchase totals =	$542.27		$583.2397	$583.25	$583.20	$583.20